The subject matter disclosed herein relates generally to the Magnetic Resonance Imaging (MRI) systems, and more particularly to a Radio Frequency (RF) coil for MRI systems.
MRI is a medical imaging modality that generates images of the inside of a human body without using x-rays or other ionizing radiation. MRI uses a magnet to create a strong, uniform, static magnetic field (i.e., the “main magnetic field”) and gradient coils to produce smaller amplitude, spatially varying magnetic fields when a current is applied to the gradient coils. When a human body, or part of a human body, is placed in the main magnetic field, the nuclear spins that are associated with hydrogen nuclei in tissue water become polarized. The magnetic moments that are associated with these spins become preferentially aligned along the direction of the main magnetic field, resulting in a small net tissue magnetization along that axis (the “z axis,” by convention) and the gradient coils encode the MR signal.
Radio frequency (RF) coils are used to create pulses of RF energy at or near the resonance frequency of the hydrogen nuclei. These RF coils are used to transmit RF excitation signals and receive MR signals used to form the images. Various types of RF coils may be used in an MRI system such as a whole-body RF coil and RF surface (or local) coils. Two common RF coil configurations are the birdcage coil and the transverse electromagnetic (TEM) coil. During an MRI scan, acoustic noise and vibration can be generated in the patient bore of the MRI system. The acoustic noise and vibration can be uncomfortable and potentially harmful to both the patient and scanner operator. There are several sources of acoustic noise in an MRI system including the gradient coils and the RF coils. The acoustic noise generated by the RF coil is typically caused by eddy currents induced in the RF coil conductors by operation of the gradient coils. In particular, current pulses are applied (e.g., as part of a pulse sequence) to the gradient coils to generate time-varying magnetic fields. These time-varying magnetic fields can induce eddy currents in an RF coil that cause motion or vibration of the RF coil and result in acoustic noise. In addition, the eddy currents induced in the RF coils can produce heat. The heat produced by the RF coils may cause an increase in the temperature of the patient bore which can affect patient comfort and the efficiency of the MRI system.